The British Computer Society has called for Phorm's targeted-advertising system to be opt-in.

Echoing calls from the Information Commissioner's Office (ICO), which earlier this month stated that Phorm's nascent service must be opt-in rather than opt-out to conform with privacy regulations, British Computer Society (BCS) government relations manager David Evans on Tuesday said that Phorm's service being opt-in would make commercial sense for the company.

"If you are making use of personal information, you should be asking to do so, and it's good practice to offer opt-in," said Evans. "If you are looking to build trust amongst customers, this is the way to do it."

Evans suggested that, at a recent "town-hall meeting" organised by Phorm, the company seemed to be pushing back against suggestions that its service should be opt-in. "Phorm seemed to be trying to resist; they seemed to have concerns that their position may not be commercially viable if they have to ask people to opt-in," he said.

However, a Phorm spokesperson on Tuesday said being opt-in had always been on Phorm's agenda.

"During the first deployment, the user will see the first screen, which will ask if they want to continue," said the spokesperson. "People will be given as much informed consent as possible. We've always been of the opinion that choice is critical and we will be as clear as possible [in getting] user consent. The first screen will clearly articulate user options."

Opt-in is already used by at least one Phorm competitor, US private start-up NebuAd.

BT is one of the ISPs that currently have an agreement with Phorm to provide its service to customers. On Tuesday, a BT spokesperson said that trials of a Phorm service, to be branded BT Webwise, will commence within 28 days.

The telecoms giant has been investigating methods of recording opt-in or opt-out status that do not require a cookie to be linked to a user's computer, said the spokesperson.

"We have been exploring a technical solution for opt-out which will not require a cookie to be placed on a customer's machine," said the spokesperson. "It will be recognised at a network level."

Servers that mirror and profile traffic that has been opted-in will be configured so they will not mirror or profile traffic that has been opted-out, said the spokesperson, who declined to give any details before the trial of exactly how the user's computer would be identified and added that BT had yet to implement the technology.

"We're optimistic," said the spokesperson. "We're hoping to have [the technology] in place by the time we do the trial." BT has already performed two trials of Phorm technology, in 2006 and in the summer of 2007, said the spokesperson. While user consent had not been obtained, the spokesperson said the trials had been of the technology behind the service.